Heat-hardened stainless steel and method for cold treating same



p 1959 .J. H. WAXWEILER 2,903,386

HEAT-HARDENED STAINLESS STEEL AND METHOD FOR COLD TREATING SAME Filed Oct. 27, 1955 800 900 I000 Il00 I200 I300 I400 I500 m n .0 mm m mmm n mm m m wew .T w o a. @R I A 27:; O O O O O m 0 o O 0 w o m m 1 m m m m m l 9 C021 503 2 2 E HT EE 3 w Sumof Austenite-Forming Elements (25000 80Mn ||5Ni 2900M) Composition of Chromium- Stainless Steel in terms of the sum of the Austenite- Forming Elements (Carbon, Monigonese, Nickel,und

Nitrogen Vs. the sum ofthe Ferrite-Forming Elements Silicon and Chromium.)

INVENTOR w, ,%m m w 6 WM 0. W H

S 6 m, J Y B United States Patent HEAT-HARDENED STAINLESS STEEL AND METHOD FOR COLD TREATING SAME James H. Waxweiler, Middletown, Ohio, assignor to Armco Steel Corporation, a corporation of Ohio Application October 27, 1955, Serial No. 543,075

11 Claims. (Cl. 148-2155) In general, the present invention relates to austenitic stainless steels. More particularly, it is concerned with hardened austenitic stainless steel articles and the method of hardening the same.

Among the objects of my invention is the provision of a stainless steel which is corrosion-resistant, ductile and readily fabricated as by drawing, forming, punching, bending and the like, and which is subsequently hardened and strengthened by moderate temperature heat-treating methods to give various products and articles which are free of scale, oxidation, surface roughening and the necessity for pickling or other treatment following the heathardening operation, and which additionally are free of sagging or other distortion occasioned by heat treatment, and moreover, which are free of directional effects commonly had in steels hardened by cold-working methods.

Other objects of my invention in part will be obvious and in part pointed out during the course of the description which follows.

My invention, therefore, resides in the combination of elements, composition of ingredients and in the various operational steps and the relation of each of the same to one or more of the others, the scope of the application of all of which is set forth in the claims at the end of this specification.

In the accompanying drawing I show the composition limits of the stainless steel articles of my invention, these being disclosed for the preferred range as well as for the broad permissible range.

Now to gain a better understanding of certain aspects of my invention it may be noted that the stainless steels have found great favor in the arts. Actually, they are used in an infinite variety of applications where strength, toughness and resistance to corrosion are required. In general, these steels are either of the straight chromium grade or the austenitic chromium-nickel grade. The former generally contains about to 35% chromium, with the remainder principally iron. Of course, there are present carbon, manganese, silicon, phosphorus and sulphur. Ordinarily these ingredients appear in minor amounts although substantial amounts of any one or more of them may be employed to achieve known desired properties. In addition, there may be included small amounts of molybdenum, tungsten, titanium, columbium or other common alloying elements for special purposes.

The steels of the straight chromium type, that is, the steels in which there is no substantial nickel content, are commonly represented by the 12% chromium, the 17% chromium and the 162 chromium-nickel grades. These steels may be hardened by heating to a temperature of Patented Sept..8, 1959 ice some 1850 to 1950 F. and then quenching either in air, water or oil. Immediate hardening is had.

It frequently is found, however, that the quench-hardening operation will adversely affect the surface conditions of the steel. And sometimes the shape also is affected. These hardening temperatures are such that heavy scaling is commonly encountered with consequent metal loss in the subsequent scale-removing processes required. Moreover, the high heat-treating temperatures are inclined to unduly soften the metal with resultant distortion.

Of the chromium-nickel grades of stainless steel, perhaps the most popular are the austenitic grades containing chromium in the amount of about 16% to 35%, nickel about 5% to 30% and remainder principally iron. These steels, of course, contain carbon, manganese, silicon, phosphorus and sulphur in minor amounts. They may however include one or more of these ingredients in substantial amounts for special purposes. They also may contain molybdenum, ttmgsten, columbium, titanium and other common alloying elements for special purposes.

These austenitic stainless steels are not generally considered to be hardenable by heat-treating methods, however. Where hardness is had, this is achieved by coldworking, as for example, cold-rolling, cold-drawing and the like, in the production of sheet, strip, special shapes, rods, wire, and the like. It is found, however, that these hardened products do not possess physical properties which are uniformly high. Actually, the physical properties taken across the direction of working differ substantially from those taken along the direction of working. In short, in the austenitic steel products in which hardening is achieved through cold Working methods there is found an objectionable directional effect.

Although, as indicated above, the austenitic chromiumnickel stainless steels are not generally considered to be hardenable by heat-treating methods, there are certain of these steels of special composition which will respond to heat-treating methods. For example, such steels in which there are included a strong carbide-forming element such as columbium or titanium are satisfactorily hardened by known methods. But these special ingredients are costly and columbium is quite rare and highly strategic. Moreover, the titanium frequently detracts from the cleanliness of the steel.

There are still other austenitic chromium-nickel stainless steels which are hardenable by heat-treating methods. These, instead of employing a strong carbideforming ele ment, include one or more of the special ingredients alu- 1 minum, beryllium or copper. These additions, too, repreened by heat-treatment at comparatively low temperatures, all without the necessity for including special hardening agents in melting the steel and without risk of. heat discoloration and sagging during hardening heat-treatment.

. Considering. now more particularly the practice of my invention, I provide an austenitic chromium-nickel stainless steel in which there are present certain critical amounts of the two ingredients chromium and nickel, together with small amounts of carbon, manganese, silicon and nitrogen. Actually, I provide a critical balance between the ferrite-forming ingredients chromium and silicon, on the one hand, and the austenite-forming ingredients nickel, manganese, carbon and nitrogen, on the other. And I find that such a steel, when solutiontreated or annealed at particular temperature, is readily transformed by cold-treatment, and hardened and strengthened by subsequent treatment at a moderate elevated temperature, a temperature however which is not sufficient to give rise to heat scaling or sagging of the metal.

I find that the steel of my invention in its annealed condition, that is, in the form in which it comes from the mill, readily lends itself to various working and forming operations such as bending, drawing, stretching and the like. In general, annealing at the mill is had at a temperature of 1400 to 2250 F., the particular temperature within this range however being correlated with the composition balance as more fully dealt with hereinafter. The annealed steel in the form of plate, sheet, strip, bars, rods, wire, extrusion shapes and tubes,

is fashioned by the customer fabricator into a variety of articles of ultimate use. Hardening and strengthening are had by first transforming the steel through coldtreatment at a temperature of about 32 to -200 F. for a period up to about 16 hours although 1 hour is usually sufficient, and then hardening by reheating to a temperature of about 750 to 1100 F. for a period ranging from about A; hour to about 300 hours. Preferably, the transformation treatment is had at a temperature of about 80 to about -125 F. for at least about /2 an hour. And the hardening is achieved by treatment at a temperature of about 800 to 900 F. for about A hour to 300 hours and preferably for a period of about 5 to 50 hours. Actually, I find that best results are had where the hardening treatment is had for at least 10 hours. Although I am particularly concerned with the production of various hard, strong articles fashioned from wrought metal products, I also provide castings such as precision castings, which likewise are hard and strong by reason of a combination of particular critical composition and particular heat treatment, the composition and heat treatment being as described above.

Considering more specifically the steel and method of my invention, the composition of the steel itself essentially consists of carbon up to .30%, manganese up to 5.00%, silicon up to 1.00%, chromium 12.0% to 21.0%, nickel 3.0% to 10.0%, nitrogen up to 0.15%, and the remainder iron. Of course it will be understood that sulphur and phosphorus are present in the usual minor amounts, although larger amounts may be employed where desired. The composition limits of my steel, however, are further qualified, this to the extent that the ferrite-forming ingredients chromium and silicon bear a particular relation to the austenite-forming ingredients nickel, carbon, manganese and nitrogen. More specifically, 80 times the percentage of the silicon content plus 77 times the percentage of the chromium content, this representing the sum of the ferrite-forming elements, bears a highly critical relationship to the sum of the austenite-forming elements, as defined by 2500 times the percentage of carbon plus 80 times the percentage of manganese plus 115 times the percentage of nickel plus 2900 times the pecentage of nitrogen. This critical balance between the sum of the ferrite-forming elements, on the one hand, and the sum of the austenite-forming elements, on the other hand, is illustrated in the accompanying drawing. The critical range is there defined by the area A, B, C and D. And I preferably broaden this highly critical range by employing a carbon content 4 in my steel of at least 08%. With this I find that the critical range is extended to the area A, B, C and D, as shown in the accompanying drawing.

As a matter of preference, the relationship between the ferirte-forming elements, on the one hand, and the austenite-forming elements, on the other, is further restricted. This restricted range is defined by the small area a, b, c and d of the accompanying drawing. Here it will be noted that a carbon content of at least .08% is desired in order to achieve maximum latitude in the preferred critical balance.

A preferred range of composition, that is, a range in which I find best results in terms of balance of such factors as the resitsance to corrosion, the ductility during Working and forming, and the ultimate strength and hardness had as a result of heat-treatment subsequent to forming, essentially consists of .08% to .10% carbon, .25% to .90% manganese, .40% to .60% silicon, 18.0% to 19.0% chromium, 4.75% to 6.05% nickel, .02% to .03% nitrogen, and remainder iron. The specific aim of the melt-shop in melting this steel is 090% carbon, .40% manganese, .50% silicon, 18.70% chromium, 5.20% nickel, .030% nitrogen, with remainder iron. Phosphorus and sulphur are present in small amounts.

Here again it will be understood that a critical relationship is preserved between the sum of the ferriteforming elements and the sum of the austenite-forming elements. This is defined by the area A, B, C and D of the drawing. Best results are had with steels in which the composition balance between ferrite-forming ingredients and austenite-forming ingredients falls within the more restricted area a, b, c and d, as noted above.

The highly critical character of the steel of interest is revealed by a comparison of the physical properties of five specific compositions answering to the requirements of the specification and four of generally similar composition but which fail to comply with the critical requirements. The five steels of critical composition are represented by the heat Nos. 10, 22, 26, 27 and 18 of the following table. Two steels in which the balance between ferrite-forming ingredients and austenite-forming ingredients are on the low-side, as seen in the drawing, and giving a steel which is too unstable, are represented by heat Nos. 5 and 20, while two steels inwhich the critical balance is on the high side, giving steels which are too stable, are represented by heat Nos. 29 and 54.

TABLE I 1 Composition analysis of nine specific chromium-nickel stainless steels A. TOO UNSTABLE Heat Percent ASTM N o. 0 Mn Si Or Ni N of Delta Grain Ferrite Size 5 067 .62 50 16.13 6.05 .030 0 l M 20 .020 .72 .56 18.62 6.12 .010 M B SATISFACTORY C. TOO STABLE Transformed to martensite so grain size could not be determined The calculated composition balance factors for each of the nine steels of Table I, that is, the factor-representing the sum of the ferrite-forming elements (silicon and chromium) and that representing the sum of the TABLE II Calculated sum of ferrite-forming elements and sum of austenite-forming elements of the nine specific comp sitions of Table l It will be seen from the drawing that the heat No. falls outside of the critical range of composition balance. The heat is too unstable for satisfactory results as appears more fully hereinafter. The heat No. 20, however, falls outside of the range A, B, C and D. And actually it would fall within the range A, B, C and D except for the circumstance that its carbon content (0.20%) is much too low. The heat No. 20, therefore, along with the heat No. 5, actually falls outside of the permissible range of composition balance and into the area where the steels are too unstable for satisfactory use, as fully established by the physical properties presented below.

The steels identified as heat Nos. 29 and 54, as seen from the drawing, fall above and outside of the critical range of composition balance. These steels lie in the range of the objectionably stable steels. This objectionable stability is fully established by the physical properties given hereafter.

All of the heats of stainless steel whose compositions are given in the Table I above and whose calculated sum of austenite-forming and sum of ferrite-forming elements are given in Table II, were annealed at temperatures ranging from 1400 to 2000 F., followed by air-cooling. And then with the exception of two of the heats (heats Nos. 5 and 20) the steels were subjected to cold-treatment at temperatures between -30 F. and 95 F., followed by reheating to 800 F. The actual annealing temperatures, cold-transformation temperatures and temperatures of reheating to achieve final hardness, together with the times of treatment are given in Table III.

It will be seen from the results given in Table II that the steels designated as heats Nos. 5 and 20 immediately harden upon cooling from the annealing temperature. Actually the steels are much too hard, respectively Rock- Well C35 and C24, for satisfactory working and forming operations. Both of these steels, as noted above, fall outside of the range of critical composition balance, as defined by the area A, B, C and D of the drawing. Since they would be excessively hard upon reaching the customer they need be given no further consideration.

Now as to the remaining steels of Tables I and II, it will be noted that all seven display some improvement in mechanical properties by virtue of the cold transformation treatment followed by hardening heat-treatment.

0 TABLE III Mechanical properties of the steels of Tables I and II in the annealed condition and inv the hardened condition had by cold-treatment followed by heat-treatment A. TOO UNSTABLE Ult. 2%Y1d. Elon. Heat Treatment Tens. Stu, 1n 2" Rock. N 0. Str., p.s.i per- Hard.

p.s.i. cent 5;... 1,050 F.2 min.air 0001.... 035 20.-.. ...-.do 024 B. SATISFACTORY 10.-.. 1,950 F.2 min.air 0001.... 171,300 46, 400 23 B91 +0001 to F.min +800 F.50 hrs 203, 200 154, 300 12 C43 22. 1,750 F.2 min-air 0001.... 145, 600 32, 400 24 B98 +0001 to 80 F.3O min. 26 +800 F.50 hrs 181, 100 147, 800 14. 5 C41 +s00 F.50 hrs -I 27.... 2,000 I .-2 min-air 0001....

+0001 to 95 F.30 min.-.. +800 F.50 hrs 18--.-

1,400 F. min-air 0001. +0001 to 30 F.30 min...- +800 F.50 hrs 144, 000

O. TOO STABLE 29.-.- 1,400 F.-90 min-air c001... B93 +0001 to -30 F.30 min. 1397 +800 F.50 hrs B97 54.-.- 1,40[) F.90 min-air 0001. B86 +0001 to 30 F.30 min.-.- B91 +800 F.50 hrs B91 The steels of heat Nos. 29 and 54, however, evidence such a slight increase in hardness that the transformation and hardening heat-treatment is of virtually no practical benefit. In connection with the steel of heat No. 29 it will be seen that the hardening operations merely resulted in an increased hardness from B93 to B97, an increase of negligible degree. And it will be seen that the steel of heat No. 54 had its hardness increased from B86 to B91, a like insignificant amount. These two steels, therefore, are seen to be much too stable. This circumstance also is reflected by the drawing, as noted above, both steels falling well outside of the range of critical composition balance.

The steels of heat Nos. 10, 22, 26 and 27 are seen to develop excellent physical properties by virtue of the correlation of composition and heat-treatment, consisting of annealing betwveen 1750 and 2000 F., then cooling to a 8O to 95 F., and reheating to 800 F. In each of these instances the yield strength increased greatly, this amounting to some 4- or 5-fold. For the illustrative steel of heat No. 10 the yield strength increased from 46,000 psi. to 154,300 psi. And it is noted that there was a corresponding increase in the hardness, this going from Rockwell B91 for the steel of heat No. 10 to Rockwell C43.

Now the steel of heat No. 18 also develops satisfactory properties but not when annealed at a temperature of 1950" F. With such a high annealing temperature I find that the steel becomes much too stable. And the stable austenitic characteristic is not altered through cold treatment followed by heat treatment. It will be seen from the data presented above that there is no percep- 7 tible change in the hardness of the steel through the successive heat-treating operations, the hardening in the annealed condition being Rockwell B93 and in the hardened condition only B94.

Actually the steel of heat No. 18, although falling within the permissible range of composition and range of composition balance as given in the drawing, falls outside of the preferred range. Both the chromium and the nickel contents are a little too high for the preferred' range of composition and the balance of the sum of the austenite-forming ingredients as compared with the sum of the ferrite-forming ingredients lies outside of the preferred range of the drawing. This steel, however, when annealed at appreciably lower temperature, that is 1400 F., for 90 minutes, is seen to transform by cold-treatment at -30 F. and harden by heattreatment at 800 F., the hardness going from Rockwell B93 in the annealed condition to C23.5 in the transformed and C31 in the fully hardened condition. It is to be noted that while the higher annealing temperature, that is 1950 F., results in an objectionable, stably austenitic condition, the anneal at 1400 F. precludes full development of the stable austenite and permits realization of the desired heat-hardening effects.

While the broad range of annealing temperature lies between 1400 and and 2250 F., I find that the specific temperature employed preferably is correlated with the sum of the ferrite and austenite factors. In general, when the sum of these two factors is on the high side, the annealing temperatures should be on the low side. For, otherwise, as noted above, the steel becomes too stably austenitic as a result of the annealing treatment. When the sum of these factors is on the low side, however, the higher annealing temperatures may be employed. In fact, they are preferably employed in order to lend a little stability to the steels which are inclined to excessive instability. The relationship between the sum of the austenite and ferrite factors, on the one hand, and the annealing temperatures preferably employed, on the other, are given in Table IV below.

TABLE IV Correlation between the annealing temperatures and the sum of austenite and ferrite factors given in Table II Where Sum is Annealing Tem- In the hardened steels of my invention it will be seen that there is achieved a yield strength exceeding 100,000 p.s.i., although the steel is in annealed condition is soft and ductible with elongation exceeding about Moreover, it is to be noted that full hardening is had at temperatures which are not excessively high. In the specific examples given the full hardness was realized at the final temperature treatment of 800 F.

It will be seen, therefore, that I provide in my invention a hard, strong, chromium-nickel stainless steel of critical composition balance, together with a method of achieving the same, which is particularly suited to the production of wrought and cast articles in whichthe metal in annealed condition may be subjected to: a variety of working, forming, shaping operations for the former and machining operations for the latter. The combination of excellent ductility in the annealed condition with great hardness and strength in the transformed and heat-hardened condition, all at moderate temperatures following the fabricating operations, assure an excellent surface free of oxidation, scaling and surface roughening.

'Ihe steels of my invention are particularly practical in that they require no special alloy additions to achieve hardness and in that they are free of the melting and teeming problems encountered with many of the hardened chromium-nickel stainless steels of the prior art. Moreover, the hardened articles and products are free of directional effects commonly encountered in the austenitic chromium-nickel stainless steel in which hard ening is bad by cold-working operations. While the steels of my invention sensitively respond to the hardening heat-treatment, they are sufficiently stable that undesired hardening in the annealed conditions is precluded.

As many possible embodiments may be made of my invention and as many changes may be made in the embodiments hereinbefore set forth, it is to be understood that all matter described herein or shown in the accompanying drawing is to be interpreted as illustrative and not as a limitation.

I claim as my invention:

1. In the production of heat-hardened austenitic chromium-nickel stainless steel of high yield strength, the

art which comprises providing a steel essentially consisting of carbon .08% to 30%, manganese up to 5.00%, silicon up to 1.00%, chromium 12.0% to 21.0%, nickel 3.0% to 10.0%, nitrogen up to .15%, and remainder substantially all iron, the relative amounts of said car-v bon, manganese, nickel and nitrogen, on the one hand, and silicon and chromium on the other, being substantially in accordance with the area A, B, C and D of the.

accompanying diagram; annealing the same at a temperature of about 1400" to 2250 F. and cooling; transforming the same by cold-treatment at a temperature of 32 to -200 F.; and then hardening by reheating to a temperature of 750 to 1100 F.

2. In the production of heat-hardened austenitic chromium-nickel stainless steel of high yield strength, the art which comprises providing a steel essentially consisting of carbon .08 %to .30%, manganese up to 5.00%, silicon up to 1.00%, chromium 12.0% to 21.0%, nickel 3.0% to 10.0%, nitrogen up to .15 and remainder substantially all iron, the relative amounts of said carbon, manganese, nickel and nitrogen, on the one hand, and silicon and chromium, on the other, being substantially in accordance with the area A, B, C, and D of the accompanying diagram; annealing the same at a temperature of about 1400 to 2250 F. and cooling; cold-treating at a temperature of about 80 to 125 F. for at least /2 an hour; and then hardening by reheating to a temperature of about 800 to 900 F. for about hour to 300 hours.

3. In the production of heat-hardened austenitic chromium-nickel stainless steel of high yield strength, the art which comprises providing a steel essentially consisting of carbon .08% to 30%, manganese up to 5.00%, silicon up to 1.00%, chromium 12.0% to 21.0%, nickel 3.0%

to 10.0%, nitrogen up to .15 and remainder substantially all iron, the relative amounts of said carbon, manganese, nickel and nitrogen, on the one hand, and silicon and chromium, on the other, being substantially in accordance with the area A, B, C and D of the accompanying diagram and with the sum of the ferrite and austenite-forming elements of that diagram from 2280 to more than 2480; annealing the same at a temperature of about 1400 to 2250 F., the particular annealing temperature being 1400 to 1700 F. when the sum of the two factors is 2480 or more, the annealing temperature being 1650 to 1950 F. when the sum of the two factors is 2480 to 2430, and being 1850 to 2250 F. when the sum of the factors is 2430 to 2280; transforming the same by cooling to a temperature of 32 to -200 F.; and then hardening by reheating to a tem perature of 750 to 1100 F.

4. In the production of heat-hardened austenitic chr0- mium-nickel stainless steel of high yield strength, the art which comprises providing a steel essentially consisting of carbon up to .30%, manganese up to 5.00%, silicon up to 1.00%, chromium 12.0% to 21.0%, nickel 3.0% to 10.0%, nitrogen up to .15%, and remainder substantially all iron, the relative amounts of said carbon, manganese, nickel and nitrogen, on the one hand, and silicon and chromium, on the other, being substantially in accordance with the area A, B, C and D of the accompanying diagram; annealing the same at a temperature of about 1400 to 2250 F. and cooling; transforming the same by cold-treatment at a temperature of 32 to 200 F.; and then hardening by reheating to a temperature of 750 to 1100 F.

5. In the production of heat-hardened austenitic chromium-nickel stainless steel of high yield strength, the art which comprises providing a steel essentially consisting of carbon .08% to 30%, manganese up to 5.00%, silicon up to 1.00%, chromium 12.0% to 21.0%, nickel 3.0 to 10.0% nitrogen up to .15 and remainder substantially all iron, the relative amounts of said carbon, manganese, nickel and nitrogen, on the one hand, and silicon and chromium, on the other, being substantially in accordance with the area a, b, c and d of the accompanying diagram; annealing the same at a temperature of about 1400 to 2250 F. and cooling; cold-treating at a temperature of about -80 to -125 F. for at least /2 an hour; and then hardening by reheating to a temperature of 750 to 1100 F.

*6. In the production of heat-hardened austenitic chromium-nickel stainless steel of high yield strength, the art which comprises providing a steel essentially consisting of carbon .08% to .10%, manganese .25% to 90%, silicon .40% to .60%, chromium 18.0% to 19.0%, nickel 4.75% to 6.05%, nitrogen .02% to .03%, and remainder substantially all iron, the relative amounts of said carbon, manganese, nickel and nitrogen, on the one hand, and silicon and chromium, on the other, being substantially in accordance with the area A, B, C and D of the accompanying diagram; annealing the same at a temperature of 1400 to 2250 F. and cooling; transforming the same by cold-treatment at a temperature of 32 to 200 F.; and then hardening by reheating to a temperature of 750 to 1100 F.

7. In the production of heat-hardened austenitic chromium-nickel stainless steel of high yield strength, the art which comprises providing a steel essentially consisting of carbon .08% to .10%, manganese .25% to 90%, silicon .40% to .60%, chromium 18.0% to 19.0%, nickel 4.75% to 6.05%, nitrogen .02% to 03%, and remainder substantially all iron, the relative amounts of said carbon, manganese, nickel and nitrogen, on the one hand, and silicon and chromium, on the other, being substantially in accordance with the area A, B, C and D of the accompanying diagram and with the sum of the ferrite and austenite-forming elements of that diagram from 2280 to more than 2480; annealing the same at a temperature of about 1400 to 2250 F., the particular annealing temperature being l400 to 1700 F. when the sum of the two factors is 2480 or more, the annealing temperature being 1650 to 1950 F. when the sum of the two factors is 2480 to 2430 and being 1850" to 2250 F. when the sum of the factors is 2430 to 2280; transforming the same by cooling to a temperature of 32 to 200 F.; and then hardening by reheating to a temperature of 750 to 1100 F.

8. In the production of heat-hardened austenitic chromium-nickel stainless steel of high yield strength articles of manufacture, the art which comprises fabricating austenitic chromium-nickel stainless steel plate, sheet, strip, bars, rods, wire, extrusion shapes and tubes, essentially consisting of carbon .08% to 30%, manganese up to 5.00%, silicon up to 1.00%, chromium 12.0% to 21.0%, nickel 3.0% to 10.0%, nitrogen up to .15%, and remainder substantially all iron, the relative amounts of said carbon, manganese, nickel and nitrogen, on the one hand, and silicon and chromium, on the other, being substantially in accordance with the area A, B, C and D of the accompanying diagram, which plate, sheet, strip, bars, rods, wire, extrusion shapes and tubes shall have been annealed at 1400 to 2250 F. prior to fabrication; transforming the same subsequent to fabrication by cold-treatment at a temperature of 32 to 200 F.; and then hardening by reheating to a temperature of 750 to 1100 F.

9. Annealed austenitic chromium-nickel stainless steel plate, sheet, strip, bars, rods, wire, extrusion shapes and tubes essentially consisting of carbon up to 30%, manganese up to 5.00%, silicon up to 1.00%, chromium 12.0% to 21.0%, nickel 3.0% to 10.0%, nitrogen up to .15%, and remainder substantially all iron, the relative amounts of said carbon, manganese, nickel and nitrogen, on the one hand, and silicon and chromium, on the other, being substantially in accordance with the area A, B, C and D of the accompanying diagram and with the sum of the ferrite and austenite-forming elements of that diagram from 2280 to more than 2480 wherein annealing is had at 1400 to 1700 F. when the sum of the two factors is 2480 or more, and is had at 1650 to 1950 F. where the sum of the factors is 2480 to 2430, and is had at 1850 to 2250 P. where the sum is 2430 to 2280.

10. Heat-hardened austenitic chromium-nickel stainless steel articles of manufacture of high yield strength and essentially consisting of carbon .08% to 30%, manganese up to 5.00%, silicon up to 1.00%, chromium 12.0% to 21.0%, nickel 3.0% to 10.0%, nitrogen up to .15%, and remainder substantially all iron, the relative amounts of said carbon, manganese, nickel and nitrogen, on the one hand, and silicon and chromium, on the other, being substantially in accordance with the area A, B, C and D of the accompanying diagram; said articles subsequent to fabrication from steel annealed at a temperature of 1400 to 2250 F. having been transformed by cold-treatment at a temperature of 32 to 200 F then hardened by heat-treatment at a temperature of 750 to 1100 F.

11. Heat-hardened austenitic chromium-nickel stainless steel articles of manufacture of high yield strength and essentially consisting of carbon .08% to .10%, manganese .25% to silicon .40% to .60%, chromium 18.0% to 19.0%, nickel 4.75 to 6.05 nitrogen .02% to 103%, and remainder substantially all iron, the relative amounts of said carbon, manganese, nickel and nitrogen, on the one hand, and silicon and chromium, on the other, being substantially in accordance with the area a, b, c and d of the accompanying diagram; said articles subsequent to fabrication from steel annealed at a temperature of 1400" to 2250 F. having been transformed by cold-treatment at a temperature of 32 to 200 F. and then hardened by heat-treatment at a temperature of 750 to 1100 F.

References Cited in the file of this patent UNITED STATES PATENTS Lena July 16, 1957 OTHER REFERENCES 

1. IN THE PRODUCTION OF HEAT-HARDENED AUSTENITIC ACHROMIUM-NICKEL STAINLESS STEEL OF HIGH YIELD STRENGTH, THE ART WHICH COMPRISES PROVIDING A STEEL ESSENTIALLY CONSISTING OF CARBON .08% TO .30%, MANGANESE UP TO 5.00%, SILICON UP TO 1.00%, CHROMIUM 12.0% TO 21.0%, NICKEL 3.0% TO 10.0%, NITROGEN UP TO .15%, AND REMAINDER SUBSTANTIALLY ALL IRON, THE RELATIVE AMOUNTS OF SAID CARBON, MANGANESE, NICKEL AND NITROGEN, ON THE ONE HAND, AND SILICON AND CHROMIUM ON THE OTHER, BEING SUBSTANTIALLY IN ACCORDANCE WITH THE AREA A,B,C AND D OF THE ACCOMPANYING DIAGRAM; ANNEALING THE SAME AT A TEMPERATURE OF ABOUT 1400* TO 2250* F. AND COOLING; TRANS- 